Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Milwaukee/Sullivan WI
324 PM CST Monday Nov 30 2015
Tonight and Tuesday...forecast confidence high.
A steady stream of warm air advection over southern WI is leading to
scattered showers this afternoon. The main precipitation band will arrive
late this afternoon in south central WI and spread northeast through
early evening. This is due to a strong leading shortwave trough
ahead of a sprawling and deepening upper low over Nebraska...
accompanied by strong warm air advection and Omega leading to
impressive q-vector convergence.
Southern WI should see about a half inch of rain during the
overnight hours. The dry slot will make its way into southern WI
Tuesday morning and diminish precipitation... likely arriving in msn by 8
am and Milwaukee by 9 and out of the mkx forecast area by noon.
There may be a short period of mixed precipitation before it ends as the
cold air wraps into the system.
The wrap-around precipitation may spread into southern WI by late afternoon
but the latest forecast soundings show moisture to be very shallow
prior to 00z. This would be in the form of snow showers possibly
mixed with rain. Clouds should hang around through the day.
Temperatures will hold steady through the day with the ongoing cold
Tuesday night and Wednesday...forecast confidence high.
The center of the stacked middle/upper low exits northeast Wisconsin
Wednesday morning and is over lower Michigan and the Northeast
Lake Huron area by Wednesday evening. The center of the 500 mb
middle level low moves across southern Wisconsin Tuesday night. This
should bring an increase in the light precipitation...before
diminishing Wednesday morning. The precipitation type would be
mainly light snow with little accumulation.
Middle levels dry Wednesday afternoon but a stratocumulus shield is
still expected with the lower level moist cyclonic flow.
Wednesday night and Thursday...forecast confidence high.
A northern stream shortwave will move across southern Canada and
the Lake Superior area Thursday.
The low levels remain moist into Wednesday night with the
stratocumulus slow to clear on the GFS. The low levels dry
Thursday morning although a narrow band of altocumulus may move
across southern wisconsinin in the warm advection associated with
the northern stream shortwave.
The GFS and European model (ecmwf) are dry with a large surface high centered over
the middle Mississippi Valley building east across the Ohio Valley.
This keeps a west flow across southern Wisconsin.
Thursday night and Friday...forecast confidence high.
Upper ridging occurs across the middle Mississippi Valley as a large
trough moves into the West Coast region of the United States
The surface ridge builds north into the Great Lakes later Friday
with a light south flow beginning Friday.
Saturday...forecast confidence high.
The large trough reaches the High Plains Saturday with a northern
stream shortwave north of Minnesota.
A south flow increases in the low levels across southern
Wisconsin with both the European model (ecmwf) and European model (ecmwf) dry. GFS forecast
soundings show a strong inversion...but in the lowest levels it
appears weak enough that the warmer European model (ecmwf) may verify better.
Sunday and Monday...forecast confidence medium.
The base of the northern stream shortwave moves quickly across
southern Canada north of the Great Lakes Sunday as the southern
stream trough moves into the middle Mississippi Valley.
A surface ridge builds back across the Great Lakes. The models
Scattered rain showers will continue through the afternoon. The next
band of rain will arrive early this evening as a very strong upper
level low pressure system approaches the region. Ceilings will drop to
MVFR levels early in the evening... and drop to IFR with the more
steady rain overnight. Temperatures will be warm enough to preclude any
threat of a wintry mix.
Ceiling/visibility improvement and dry weather will arrive Tuesday morning
with a wedge of dry air wrapping around the upper low. Scattered
snow showers will be possible across southern WI from late Tuesday
afternoon through Wednesday afternoon. Little or no accumulation
Increasing easterly winds and waves are resulting in Small Craft
Advisory conditions late this afternoon. These will persist through
tonight. The winds and waves will subside for a time late tonight
into early Tuesday morning...before westerly winds increase to Small
Craft Advisory conditions again by middle to late morning on Tuesday.
Therefore...the Small Craft Advisory is in effect through Wednesday
morning...despite the short pause as winds reconfigure from easterly
Lm...Small Craft Advisory from 3 PM this afternoon to 6 PM CST
Tuesday for lmz643>646.
Tonight/Tuesday and aviation/marine...mrc
Tuesday night through Monday...hentz